The body of a human being is governed by his/her brain. Understanding and monitoring brain activity could potentially improve the quality of life and work efficiency. Monitoring brain activity may, for example, aid in the cure of sleep disorders; in detecting sleep onset during attentive tasks such as driving; in detecting pilot blackout or disorientation in flight; in monitoring attention and consciousness; in and sensing brain activity of those not otherwise able to communicate.
All of these applications require portable devices that sense brain activities or status of consciousness. The brain works by communication between the neuron cells, which emit electrical pulses and thus produce an electrical field and an accompanied magnetic field. A current source in the neurons results in a current and thus causes an electrical field on the scalp. A corresponding potential difference may be detected (measured with EEG). Similarly, a magnetic field outside the head may be detected (measured with MEG). By measuring the electric or magnetic field, the activities of the brain can be detected.
As such, two known methods may be used to sense human brain activities—electroencephalography (EEG) and magnetoencephalography (MEG), which work by measuring the electric and magnetic fields corresponding to the brain activities, respectively. In EEG, electric signals measured through a set of electrodes (placed on the scalp of the subject) are amplified, digitized, and interpreted by using EEG software that creates real-time brain waves. In MEG, the data is a measurement of the accompanied magnetic field generated by the same electrical currents that produce the EEG data, and roughly resembles EEG recordings. Both EEG and MEG can be used to interpret brain activity. However, most existing EEG devices are suitable only for clinical or laboratory applications since the electrodes must be in contact with the subject's scalp. MEG measurement is non-contact and non-invasive and thus it could be suitable for both clinical and non-clinical applications.
However, the magnetic field intensity of the brain is very weak (typically at the level below 10−12 Tesla), therefore conventional methods of measuring magnetic fields, such as the field detection coils, the Hall element, the magneto-resistance (MR) element, the giant magneto-resistance (GMR) element, and the thin film fluxgate sensor (FGS) are not sensitive enough to detect the magnetic field of the brain.
The Superconducting Quantum Interference Device (SQUID) has remained to be the only commercially available medical apparatus that can detect the magnetic field of the brain. However, Since the SQUID uses field detection coils made of superconducting material operated at temperature—269° C. with circulated liquid helium cooling, it requires a huge cooling system and a magnetic shielding room, and thus its applications are limited to laboratory and dinical conditions.
It is expected that portable MEG devices equipped with micro MEG sensors have a potential for a spectrum of applications of non-contact sensing and monitoring of brain activities or status of consciousness.
Accordingly, there is a need for improved magnetic field sensors, and methods.